There are several significant processes for making mixed alcohols from synthesis gas or H.sub.2 /CO. For example, British patent publication No. 2,083,469 discloses such a process wherein the catalyst is based on chromium, zinc and at least one alkali metal. While the applicants claim that the mixed alcohols may contain from 35 to 75 weight percent methanol, the examples given vary from 43 to 69 percent methanol.
The Dow Chemical Company in U.S. Ser. No. 622,029, filed June 18, 1984, now abandoned which is a continuation-in-part of Ser. No. 476,674 which was filed March 18, 1983, now abandoned, both of which are hereby incorporated by reference, and PCT application 84.00405 filed Mar. 16, 1984 published Sept. 27, 1984 as 84/03696 which is also incorporated herein by reference, discloses a process for making mixed alcohols from synthesis gas using a molybdenum-based catalyst.
Substantial methanol may be coproduced with the higher alcohols in these processes. The coproduction of methanol may be undesirable for a number of reasons. At the time this application is being filed, methanol prices are depressed due to oversupply and it is available for a price substantially lower than any of the higher alcohols.
The major targeted use for the synthesized mixed alcohols is as a fuel additive in gasoline engines. Some have held that methanol is an undesirable component for a number of reasons. When blended in hydrocarbon gasolines, methanol is said to increase evaporative emissions and to be liable to phase separation which may lead to corrosion of fuel systems and engine components and possible inferior drivability. While these deficiencies may be in dispute, it is at least desirable to minimize or at least reduce coproduced methanol.
One remedy is to make a lower percentage of methanol in the mixed alcohols. U.S. Ser. No. 635,999, filed July 30, 1984, now abandoned, which is incorporated herein by reference, discloses that one may vary the ratio of methanol to higher alcohols in a mixed alcohols process using a molybdenum-based catalyst by adjusting the concentration of a sulfur-releasing substance in the feed. As the concentration of the sulfur-releasing substance is adjusted upwards, the percentage of methanol in the mixed alcohols produced is lowered. However, in addition, as the sulfur concentration of the feed is increased, the catalyst becomes less active for making alcohols. The minimum practically obtainable weight percentage of methanol in the mixed alcohols at the time of this filing is about 30 percent by this method.
One may also lower the percentage of methanol in the mixed alcohols through catalyst selection. In U.S. Ser. No. 636,000, filed July 30, 1984, now abandoned, which is hereby incorporated by reference, the applicant discloses a catalyst which comprises a first component which may be molybdenum or tungsten, a second component which may be iron, cobalt or nickel, a third component comprising an alkali or alkaline earth element with an optional fourth component being a support. Within certain limits as one increases the ratio of the second component to the first component, the percentage of methanol in the mixed alcohols decreases. One may achieve a methanol content as low as about 10 weight percent at practical productivities using the disclosed catalyst.
It would be desirable to make a lower methanol to higher alcohols ratio at a high productivity and without lowering the activity or selectivity of the catalyst to mixed alcohols.